1. Field of the Invention
This invention pertains to the field of energetic emulsions, and further pertains to related articles of manufacture and methods.
2. Description of the Related Art
Conventional emulsion explosives are water-in-oil emulsions, in which a discontinuous phase of inorganic oxidizer salt solution droplets is dispersed in a continuous organic fuel phase. The droplets, which constitute a dispersion or emulsion phase, are held in place by a water-in-oil emulsifier provided the emulsified state remains stable. An emulsifier (or surfactant) is usually included in the emulsion for promoting formation and stability of the discontinuous phase.
The excellent detonation velocity characteristic of emulsion explosives makes this class of explosives particularly important and contributes to its wide used. For example, detonation velocities of cap-sensitive emulsion explosives have been approximated to be in the range of 18,000 to 25,000 feet per second (5490 m/s to 7620 m/s). The reason for the high detonation velocity of emulsion explosives is the intimacy of mixing of the emulsion explosive. The continuous phase of fuel surrounds each discontinuous phase droplet of inorganic oxidizer, providing an extremely large interfacial surface area between the two phases.
Three major drawbacks reduce the effectiveness and utilization of emulsion explosives. The first drawback is that conventional emulsion explosives have relatively low densities, which limits the detonation pressure of the explosive. The low density is attributable to the addition of glass microballoons, which are added to the emulsion to increase sensitivity. The second drawback is the use of water to dissolve the inorganic salt oxidizer. Water is inert, and therefore does not add energy to the reaction. In fact, heat generated by the reaction of the energetic components is partially consumed due to vaporization of water. The third drawback is that inorganic salt oxidizers such as ammonium nitrate are in a meta-stable state when the emulsion is formed (usually at elevated temperature). Ambient temperature is below the saturation point of many commercially available emulsion explosives, thus requiring that the explosives be kept in a warm atmosphere to avoid crystallization of the oxidizer. Surface tension of the droplets is relied upon to keep the ammonium nitrate in solution. If the temperature becomes too low, the driving force of crystallization exceeds that of surface tension. Thus, crystallization is particularly likely in cold environments and during temperature cycling, such as daily ambient temperature variations and seasonal ambient temperature changes. The crystallized ammonium nitrate has a needle-like shape that may puncture nearby droplets, causing the droplets to collapse and the ammonium nitrate crystals to agglomerate. Eventually, the emulsion is destabilized and the usefulness of the emulsion explosive is reduced or lost, e.g., the emulsion explosive can be rendered undetonable.